Apparently multiple suspicious packages were found downtown after the bombing, but I've heard nothing about them being actual bombs, so they were probably decoys. That the youth camp was on an island only accessible by air or boat made it ideally suited for his purpose, but he was only able to inflict the damage he did because he had a convincing police uniform and ID, set off a bomb downtown to provide a plausible reason for an armed policeman to be on the island, then used his masquerade to get people to willingly gather around him inside a building so he could shoot them while the local SWAT team was ignorantly occupied downtown. He seems to have spent YEARS preparing for this attack while all his friends and acquaintances were blissfully unaware of what was to come. It's one thing when a neighbor or coworker just snaps one day, but it's frightening to think of someone working in your office or shopping at your grocery store every day for months before driving home to the house next to yours so he can continue plotting his murder spree.

For what it's worth, I'm also told that witnesses on the island insist they saw more than one gunman; granted the conditions were chaotic, but combined with Brieviks claims (however unbalanced) that he was part of a larger group it's cause for concern we're far from the end of this.